Perfluoropolyethers are highly regarded in the specialty lubricant field because of their long liquid range, (i.e. liquid over a wide range of temperatures) low vapor pressure and high thermal and oxidative stability. Because of these properties, they are excellent high performance lubricants and have many other uses as oils, waxes, greases, hydraulic fluids and heat transfer fluids.
Commercially available perfluoropolyethers are produced by the polymerization of hexafluoropropylene oxide (DuPont KRYTOX.TM. and by photooxidative polymerization of perfluoro-olefins, utilizing oxygen and ozone (Montedison FOMBLIN.TM.). Each product has an advantage over the other. The KRYTOX.TM. fluids which have a regularly branched structure have superior high temperature thermal stability (10.degree.-15.degree. F.) over FOMBLIN.TM. fluids. The FOMBLIN.TM. fluids, random polymers having O--C--O units in their backbone, have a slight advantage (10.degree.-15.degree. F.) in their longer liquid range at low temperature.
Two very interesting analytical themes seem to be developing in the analysis of lubrication properties and thermal stabilities of perfluoropolyethers. Many researchers feel that the unusual liquid properties of the random Fomblin Z copolymer is a direct result of the inclusion of difluoromethylene oxide (CF.sub.2 O) linkages in the polyether which provide hinge-like flexibility. Another view is that the higher thermal stability of the perfluoropropylene oxide polymers results in some way from the branching (trifluoromethyl group) in the polymer. An emerging view is that the difluoromethylene unit causes the lower thermal stability of the Fomblin Z material with respect to the KRYTOX.TM. material.